how can you tell that your bake calipers are bad or going bad
The common failure mode is corrosion, causing the pistons to stick, resulting in brake drag.
The way I usually tell is by poking my finger through the wheel to see how hot the rotor is after normal driving. I have blistered several fingertips. You’d think I would learn.
If the caliper pistons don’t retract smoothly back into the calipers when replacing the brake pads, it’s time for new calipers.
Tester
A quick check…Jack the suspect wheel off the ground. Press firmly on the brake pedal to "set the brakes. Release the pedal and see if you can spin the wheel with your hand…if it’s locked or very hard to turn, the caliper is stuck / jammed. Calipers must be free to “float”, move, on their mounts…The caliper itself might be serviceable but just jammed on its mounts by dirt and corrosion. In this case, the “fixed” pad will be worn more than the pad that rests on the caliper piston…
When you perform the test above, don’t expect the wheel to turn freely…There will be some drag, that’s normal…As you drive steering loads flex the spindle, wheel bearings, rotor enough to retract the pads off the rotor just a little, reducing the drag to almost nothing. But for this to happen, both the caliper and its piston must be free to move…